A preventive medicine/wellness specialist is a physician who, through additional training, has become an expert in methods for maintaining good health and preventing disease. These specialists are the doctors people see when they are generally well or without a specific ailment and want to either learn how to maintain their current health or acquire better health.
These doctors will advise patients on specific diets, exercise regimens, and lifestyle habits that are suited to their particular needs. Preventive medicine/wellness specialists take into account a patient's nutrition deficiencies, physical and cardiovascular capabilities, and habits in order to advise specific vitamins and supplements to take, how much physical activity to undertake, and which habits should be broken and replaced with more positive behavior.

An internist is a physician who focuses on the diagnosis and treatment of conditions that affect the adult population—both acute and chronic.
These doctors are often who adults see as their primary physicians because they treat a broad range of illnesses that do not require surgical or specialist interventions. They also work to help a patient maintain optimal health in order to prevent the onset of disease.
In addition to treating the common cold and flu, internists also treat chronic diseases like diabetes and heart disease.

An ophthalmologist has the training to do much more than just prescribe glasses. They are physicians specially trained to diagnose and treat disorders of the eyes and vision. These doctors are experts on the complicated anatomy of the eye and are trained to treat eye diseases through both medical and surgical methods.
Some common conditions that ophthalmologists treat are cataracts, glaucoma, strabismus, diabetic retinopathy, macular degeneration and amblyopia. In addition, ophthalmologists can provide prescriptions for eye glasses and contact lenses and perform LASIK surgery and other corrective surgeries for refractive errors like myopia (near-sightedness), hyperopia (far-sightedness), astigmatism and presbyopia.